i965/fs: support doubles with UBO loads

i965/fs: support doubles with UBO loads

UBO loads with constant offset use the UNIFORM_PULL_CONSTANT_LOAD
instruction, which reads 16 bytes (a vec4) of data from memory. For dvec
types this only provides components x and y. Thus, if we are reading
more than 2 components we need to issue a second load at offset+16 to
read the next 16-byte chunk with components w and z.

UBO loads with non-constant offset emit a load for each component
in the vector (and rely in CSE to fix redundant loads), so we only
need to consider the size of the data type when computing the offset
of each element in a vector.

v2 (Sam):
- Adapt the code to use component() (Curro).

v3 (Sam):
- Use type_sz(dest.type) in VARYING_PULL_CONSTANT_LOAD() call (Curro).
- Add asserts to ensure std140 vector alignment rules are followed
  (Curro).

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>